title: Low-tilt monophasic and biphasic waveforms compared with standard biphasic waveforms in the transvenous defibrillation of ventricular fibrillation.
abstract: BACKGROUND
  Commercially available implantable defibrillators utilize a high-tilt waveform. Studies in atrial fibrillation and transthoracic defibrillation of ventricular fibrillation (VF) have shown improved defibrillation efficacy using low-tilt (LT) waveforms. We investigated the feasibility, efficacy, and safety of a LT waveform in the transvenous defibrillation of VF and hypothesized that it would be more efficacious than standard tilted biphasic (STB) waveforms.
  
  
  RESULTS
  The investigation was performed in four phases in a porcine model: an efficacy study of LT monophasic waveforms (n = 9), an efficacy study of LT biphasic waveforms (n = 9), a comparison study between the most successful LT waveforms and clinically available STB waveforms (n = 15), and a safety study (n = 9). A total of 1,056 shocks were delivered (phase 1: 288, phase 2: 288, phase 3: 480). The LT biphasic 8/4-ms waveform was significantly more likely to successfully defibrillate than the LT monophasic and STB waveforms with an odds ratio of 122.3 (95% confidence interval: 32.5, 460.2, P < 0.001). The calculated defibrillation threshold (E50) for the LT 8/4-ms waveform was 12.7 J compared to 43.5 J and 45.5 J for STB waveforms 6/6 ms and 8/4 ms, respectively, and 47.7 J for LT 12-ms waveform. The LT 8/4-ms waveform had no lasting detrimental effect on cardiac function, and any transient hemodynamical or biochemical changes observed were comparable to those observed with STB waveforms.
  
  
  CONCLUSIONS
  LT waveforms are effective and appear safe in transvenous defibrillation in a porcine model of VF. The LT biphasic 8/4-ms waveform is more efficacious than conventional waveforms.
authors.affiliation: Heart Centre, Royal Victoria Hospital, Belfast, UK; Queen's University, Belfast, UK.
authors.forename: Johan R
authors.initials: JR
authors.lastname: Bennett
authors.forename: Karen M
authors.initials: KM
authors.lastname: Darragh
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Walsh
authors.forename: Desmond J
authors.initials: DJ
authors.lastname: Allen
authors.forename: Michael
authors.initials: M
authors.lastname: Scott
authors.forename: Michael
authors.initials: M
authors.lastname: Stevenson
authors.forename: Jennifer A A
authors.initials: JA
authors.lastname: Adgey
authors.forename: John M C J
authors.initials: JM
authors.lastname: Anderson
authors.forename: Ganesh
authors.initials: G
authors.lastname: Manoharan
mesh_terms: D000818:Animals; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004554:Electric Countershock / Q000009:adverse effects / Q000379:methods*; D004562:Electrocardiography / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013552:Swine; D013813:Therapy, Computer-Assisted / Q000379:methods*; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000175:diagnosis* / Q000517:prevention & control*
keywords: defibrillation; low tilt; ventricular fibrillation; waveform